1. Field of the Invention
This invention relates to torsion damping devices, particularly for motor vehicle clutches, of the kind comprising two coaxial parts mounted for rotation relative to one another within the limits of a determined relative angular movement sector, and elastic means circumferentially interposed between the said parts.
2. Description of the Prior Art
Torsion damping devices of said kind make it possible to achieve regulated transmission from one of their coaxial component parts to the other of any torque which may be applied to one of the parts in question, that is to say to filter the vibrations, particularly sound vibrations, which may otherwise occur along the entire kinematic chain in which they are installed.
They are in particular used in certain clutches, particularly for automobile vehicles, in the form of a clutch friction unit usually known as a damping hub clutch friction unit, one of their parts then carrying a friction disc adapted to be gripped between two elements rotationally fixed to a first shaft, for example a drive shaft, while the other part is rotationally fixed on a second shaft, for example a driven shaft.
It is known for friction means adapted to introduce a "hysteresis" effect into the operating characteristics of a torsion damping device of this kind to be inserted between the two coaxial component parts of the device; for the same angle of movement between the said parts this hysteresis effect results in a difference between the value of the torque transmitted between these parts when the said movement takes place in a first direction, usually known as the direct direction, and the value of this torque transmitted when this movement takes place in the opposite direction, generally called the reverse direction.
It is in fact found that for certain applications a hysteresis effect of this kind contributes towards limiting vibrations and noise emitted by all the rotating elements associated with the kinematic chain to which the driving and driven shafts in question belong.
It is also known for the elastic means circumferentially interposed between the coaxial component parts of a torsion damping device of this kind to be divided into a number of separate groups, usually known as stages, for the purpose of spaced intervention of these groups all along the sector of relative angular displacement between the said parts, and for specific friction means to be associated with one or more of these groups or stages.
This arrangement enables not only the value of troque transmissible between these parts but also the hysteresis effect associated therewith to be modulated along the sector of angular movement of the coaxial parts in question, this hysteresis effect depending particularly on the magnitude of the action of the friction means used, and therefore in practice on the number of friction washers actually used for a determined angle of movement between the said parts.
This hysteresis effect nevertheless also depends on the elastic load to which these friction means are subjected.
In hitherto known torsion damping devices of the kind in question this load is most usually developed by elastic clamping means which have an axial action and which, since they bear against one of the component coaxial parts of a device of this kind, act in the direction of the other of these parts.
Since the two parts in question are not only angularly movable in relation to one another, but also axially movable in relation to one another, this has the effect that these elastic clamping means having an axial action are applied indiscriminately to all the friction means, in practice friction washers, inserted axially between the said parts.
In this case it is thus not possible to make use of these elastic means having an axial action to modulate accordingly the hysteresis effect due to the corresponding friction means.
It is true that it has already been proposed that the elastic clamping means having an axial action which are associated with any friction washer should bear against that one of the component coaxial parts of the corresponding torsion damping device which is the part with which the said friction washer is in contact, this arrangement making it possible for a particular elastic load to be associated with the friction washer in question when the latter intervenes, this particular elastic load coming into action only for this intervention.
The arrangements thus already proposed are however relatively complex in use.
It has already been proposed that the elastic clamping means having an axial action which are associated with a friction washer should bear against a transverse shoulder turned towards one of the guide washers and that they should urge the said friction washer in the direction of this same guide washer, this arrangement also making it possible for only a particular elastic load to be associated with the friction washer in question.
However, apart from the fact that in the corresponding arrangement this friction washer is not interposed axially between the two respective parts of the torsion damping device in question, and in particular is situated outside the space contained between the guide washers of the said device, which cannot fail to increase its axial dimensions, the transverse shoulder against which bear the elastic clamping means acting on the said friction washer is formed on parts specifically attached for the purpose to one of the guide washers, which also cannot fail to increase the cost of the entire device.